This program encompasses a group endeavor between physicians, physiologists, biomedical engineers, and mathematicians in a collaborative effort to investigate the electrophysiological and mechanical function facets of cardiovascular disease in children. The electrophysiological studies include investigation of intracellular- extracellular potential relationships of propagating excitation waves, the development of techniques to elucidate mechanisms of arrhythmias (re-entry versus repetitive firing), the relationship between the epicardial potential distribution and the total body surface potential distribution, the potential distribution intramurally in the ventricle in the intact animal, and the use of isopotential surface maps in animal and human studies to view the total surface potential distribution in normal and abnormal conditions. One of the basic goals of the electrophysiological work is solution of the forward and inverse electrocardiographic problem for the total torso and intact heart and a similar solution for complex networks at a local tissue level in regard to extracellular and intracellular wave forms. The cardiac contractility studies concentrate on a search for a reliable index of cardiac contractility. These studies involve in vitro measurements of force-frequency relationships in cardiac muscle in numerous species and currently focus on P max as the only reliable index of contractility. The phylogenetic studies on contractility will be used as a base to evaluate cardiac function throughout all stages of cardiac development from the embryonic heart to the newborn state. Most recently, studies have been instituted in the application of new heat jump techniques. This new experimental method as applied to study of cardiac tissue is being developed in order to explore its application for unique methods to study cardiac mechanical and electrical phenomena.